The objective of this study is to apply genetic principles as a tool in assessing the mechanisms of intestinal epithelial cell and erythrocyte transport of amino acids. By kinetic analysis of transport characteristics in normal and variant individuals and by analysis of the modes of inheritance of these characteristics, information will be gained on these processes and on their control by sodium ion. Specific aims will include the determination of variation in transport function between individuals in closed random-bred flocks of chickens, between individuals in various inbred lines of chickens and also in inbred strains of the mouse. Kinetic analysis will include comparisons in the rates of absorption in the gut and in erythrocytes at specific substrate concentrations for a series of amino acids which react with given transport systems, in data derived from Linewater-Burk analysis (kinetic constants), in specificity data (competitive inhibition studies) and in the dependence of the rate on sodium ion. Attention will be paid to normal inter-animal variability and uptake extremes found in the various normal and metabolic mutant strains. Other aims will include breeding of strains selected on the basis of high and low uptake characteristics. Dietary manipulation of limiting nutrients will allow for selection under stress. Such strains will serve as models for analysis of transport.